1. Field of the Invention
The present invention relates to a semiconductor memory device including a memory cell array configured of memory cells, a plurality of which is arranged respectively in a row direction and a column direction, each memory cell including a variable resistance element that stores information based on an electric operational property in which an electric resistance changes by application of electric stress.
2. Description of the Related Art
A non-volatile memory represented by a flash memory is used as a large-capacity and compact information storing medium in various fields such as computers, communications, measuring appliances, automatic controllers and living appliances used around a user, and a demand for a non-volatile memory that is cheaper and has larger capacity is extremely large. This is because it can perform a function as a memory card that can easily be carried around, or data storage or a program storage, etc. that stores initial settings for device operation such as a cell phone in a non-volatile manner, due to being capable of being electrically written and that data is not erased even when the power is turned off.
Note that, since the flash memory requires longer time for an erasing action of erasing data to a logical value “0” compared to a programming action of programming data to a logical value “1”, it is not capable of high-speed operation. In regard to the erasing action, when the erasing action is performed, although improvement in speed is attempted by performing in a unit of a few bytes or a block unit, there is a problem that a random access programming cannot be performed since the erasing action is performed in the unit of the few bytes/block unit.
Due to this, currently a new type of non-volatile memory that replaces the flash memory is being widely studied. Among such, a resistance change memory that uses a phenomenon in which a resistance change occurs due to application of a voltage to a metal oxide film is useful compared to the flash memory in regards to a scaling limit, and since it is capable of a high-speed data writing, it is frequently researched and developed in the recent years (e.g., refer to Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002-537627, or H. Pagnia et al., “Bistable Switching in Electroformed Metal-Insulator-Metal Devices”, Phys. Stat. Sol. (a), vol. 108, pp. 11-65, 1988, and Baek I. G. et al., “Highly Scalable Non-volatile Resistive Memory using Simple Binary Oxide Driven by Asymmetric Unipolar Voltage Pulses”, IEDM2004, pp. 587-590, 2004).
As programming/erasing properties of such a variable resistance element having the metal oxide, in a case with a driving method called bipolar switching, since the electric resistance of an element increases (high resistance state)/decreases (low resistance state) by applying voltage pulses with opposite polarity respectively to the element, it can be used as a memory by assigning a logical value as data to each electric resistance state.
As a feature of the variable resistance element having the metal oxide, it is capable of the high-speed random access programming/erasing.